A light microscopic and immunohistochemical evaluation of scars

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Abstract
Background: Scars are commonly encountered by dermatopathologists and usually do not present a diagnostic challenge. However, in some cases, the pathologist may need to consider a broad differential diagnosis including fibrohistiocytic tumors, smooth muscle tumors, myofibroblastic proliferations and desmoplastic malignant melanoma. Although specific histologic aspects of scars have been well studied, a complete histochemical profile of scars, especially at various stages of evolution, has not been described.Methods: Twenty‐five cases of scars including 8 normal scars, 5 hypertrophic scars and 12 keloids were studied. Sections were examined with Verhoeff van Giesson, colloidal iron, Giemsa, smooth muscle actin (SMA), CD34, Factor XIIIa and S‐100.Results: All scars were negative for CD34 expression. Factor XIIIa immunostaining identified only rare dermal dendrocytes. S‐100 was absent in 23 of 25 cases and stained scattered cells (less than 10%) in the other 2 cases. SMA was positive in 14 of 25 cases with 6 of these showing staining of up to 50% of spindled cells. Elastic fibers were markedly reduced or absent in all cases, mucin showed moderate or marked staining in three‐fourths of the cases and dermal mast cells showed a moderate increase in 5 cases.Conclusions: These findings confirm prior reports that negative staining with CD34, Factor XIIIa and S‐100 can help differentiate scars from dermatofibrosarcoma protuberans, dermatofibroma and desmoplastic malignant melanoma, respectively. SMA staining is much more variable and requires careful interpretation.

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